1. Field of the Invention
The present invention relates to a contact type image sensor that is used in a facsimile or a letter or image read input apparatus.
2. Description of the Prior Art
Generally, the letter or image read input apparatus using a line sensor is so constructed that the information of an original copy illuminated by a fluorescent lamp or a light emitting diode (LED) array is image-formed on the sensor through an optical lens, a rod lens array or an optical fiber so that the original or sensor is moved to read the two-dimensional information. Such a conventional read input apparatus is constructed as a combination of a charge-coupled device (CCD) with the optical lens, or the combination of a long image sensor with the rod lens array and optical fiber array. Especially, the latter, called a contact type image sensor, has hitherto been in progress of development aiming at miniaturization and low manufacturing cost of the facsimile or the like.
However, most of the contact type image sensors perform an image-formation on the sensor through a rod lens array, thereby naturally limiting miniaturization. In such type, the original must be apart from the sensor only by the conjugate length of a rod lens array; usually, it is 20 to 30 mm in thickness as a unit of usual contact-type image sensor. Furthermore, the problem is created in that the use of such a lens system requires an optical adjustment and when read, chromatic aberration must be considered because light quantity transmission efficiency is low.
On the contrary, the sensor using an optical fiber array without such a lens system requires no optical adjustment, is large enough in light quantity transmission efficiency, and not focused, whereby the optical fiber is reducible in length so as to be suitable for microminiaturization. Furthermore, when color-read, no chromatic aberration occurs, so that the sensor is very effective. However, light incident on the optical fiber at an angle larger than an angular aperture does not create total reflection at the boundary with a clad and is transmitted to the adjacent fiber therethrough. When the optical fiber array transmits the image, leakage of the light leads to deterioration of the picture quality. Accordingly, with the aim of abosorption of the leakage light, an optical fiber array of extra mural absorption (EMA) type interposing an absorber between the optical fibers is designed, but when the array is used in the contact type image sensor, the problem is created in that the original to be read cannot be illuminated.
Also, in cases where a light-permeating substrate, such as a glass substrate, is used for a substrate on which a thin-film light-detecting element array if formed, the light from a light source, when entering into the light-permeating substrate and being incident directly on the thin-film light-detecting element array without passing through the original, becomes the leakage light, thereby creating the problem in that the leakage light deteriorates the read image.